gh-117807: Handle invalid UTF-8 in mimetypes comments

Lib/mimetypes.py

@@ -237,7 +237,7 @@ def read(self, filename, strict=True):
         list of standard types, else to the list of non-standard
         types.
         """
-        with open(filename, encoding='utf-8') as fp:
+        with open(filename, encoding='utf-8', errors='replace') as fp:
             self.readfp(fp, strict)
 
     def readfp(self, fp, strict=True):
@@ -428,7 +428,7 @@ def init(files=None):
 
 def read_mime_types(file):
     try:
-        f = open(file, encoding='utf-8')
+        f = open(file, encoding='utf-8', errors='replace')
     except OSError:
         return None
     with f:

Lib/test/test_mimetypes.py

@@ -67,9 +67,33 @@ def test_read_mime_types(self):
         with unittest.mock.patch.object(mimetypes, 'open',
                                         return_value=fp) as mock_open:
             mime_dict = mimetypes.read_mime_types(filename)
-            mock_open.assert_called_with(filename, encoding='utf-8')
+            mock_open.assert_called_with(filename, encoding='utf-8',
+                                         errors='replace')
         eq(mime_dict[".Français"], "application/no-mans-land")
 
+    def test_read_mime_types_invalid_utf8_comment(self):
+        with os_helper.temp_dir() as directory:
+            data = (b"# non-UTF-8 comment: \x83\n"
+                    b"x-application/x-unittest pyunit\n")
+            file = os.path.join(directory, "sample.mimetype")
+            with open(file, "wb") as f:
+                f.write(data)
+
+            mime_dict = mimetypes.read_mime_types(file)
+            self.assertEqual(
+                mime_dict[".pyunit"], "x-application/x-unittest")
+
+            db = mimetypes.MimeTypes()
+            db.read(file)
+            self.assertEqual(
+                db.guess_file_type("sample.pyunit")[0],
+                "x-application/x-unittest")
+
+            mimetypes.init(files=[file])
+            self.assertEqual(
+                mimetypes.guess_file_type("sample.pyunit")[0],
+                "x-application/x-unittest")
+
     def test_init_reinitializes(self):
         # Issue 4936: make sure an init starts clean
         # First, put some poison into the types table

Misc/NEWS.d/next/Library/2026-06-10-00-00-01.gh-issue-117807.Cx1178.rst

@@ -0,0 +1,2 @@
+Fix :mod:`mimetypes` initialization from MIME map files containing invalid
+UTF-8 bytes in comments.